2025 350h
Car parked in garage 24 hours ago. I walk into the garage now and there is a buzzing noise coming from under the hood. Any idea what’s going on there?

 

Hybrid doing its own thing. Do not worry about it, it should go away in a few minutes.

 

You walked into the garage with your keyfob or smartphone in your hand?

The car may 'see you' and is getting prepared for your next drive. My 350H does this when I enter my garage with my fob in my pocket. As I get within a foot or so of the car I can hear something coming alive with it and if it's dark my door handle lights illuminate too. Although I can't say it happens everytime, not sure what it's doing though? I think it only makes sounds if it hasn't been driven for a while and it is not warmed up by any means, so coolant would not be warm at all. If I drive it out of my garage, drive a few klicks to the store, upon my return to car to go back it doesn't normally make any sound though.

 

No key fob near. Something was running. Near the fan area. But not the fan. Unlocked and locked the doors. No change. Started the car and let it run for a couple of minutes. Turned it off and the noise stopped. Has not made that noise since. I'm going to take a video next time trying to isolate the noise. If it happens again. Something didn't seem right with that noise going on for hours.

 

If I can remember I'll take a sound recording too when I head towards the car with my fob. I'm in Ontario and today it's fu**ing cold out (-12C or 10F), so rest assured it's not warmed up! hopefully mine will make the sound I hear.

 

Mine was in a 40 deg F garage when it was making the noise.

 

Here is my sound bite of under hood buzzing when I open up my car. First you here me unlocking and opening drivers door, very soon afterwards you here sound under hood. It stopped rather quickly, then you here me locking it back up. It's very brief starting at 2 and going to 3 second mark.

 

Brake booster pump. Since hybrids can't depend on engine vacuum or engine driven pumps, they have a separate electric pump and these pumps will prime the system prior to system start. Its a major reason why if you're doing your own brake bleeding or fluid replacement on a hybrid, that you keep all the keys well away from the car and never open the driver's door as detecting the key or having the driver's door opened will trigger the pump to prime. If this happens with a bleeder open, you've gone down the rabbit hole.

 

Ah yes! I was racking my brains what it was.

I actually initially recorded it and accidentally deleted it instead of forwarding it to my email. The second attempt about 10 minutes later and the length of time it made the sound was considerably less as you can here. And that makes perfect sense, first attempt car had sat for over a day and pressure would have bled down so it took longer time to bring it up. Second go it was almost there so it just operated for like a second and it was back up to set pressure!

I don't think it would take longer than 5 seconds though to repressurize it though so not sure if OP sound lasts longer than that. I can hop in my car and within a few seconds I get a READY light which means 'lift off!' I can put it in drive and go.

 

My 2025 Lexus NX 450+h is currently at the dealership service center. I also experienced walking into my garage to hear a buzzing noise from the rear of the car after the car had been off for 4 hours. The key fob was in the house, the car was not being charged. The car was in their shop for all of one hour when they reported they could find nothing wrong and that it is probably the electronic parking brake engaging. They told me to come pick up my car. I know nothing about cars, but I am not buying this explanation. I told them to keep the car over the weekend and check it out again on Monday. I have contacted the service rep and asked him to have them see if they could identify it as the EVAP system or possibly a faulty relay. I fear that they will blow me off as an elderly woman who doesn't know anything. It may be a perfectly normal function of the car, I just want confirmation that I have nothing to be concerned about. Electronic brake? I think not.

 

I am making an assumption here, no disrespect to anyone here. The systems that these highly sophisticated cars have in them are mind boggling to be sure. The latest safety and driving assist features, latest technical features to help improve energy consumption, battery health, gas mileage, are all very complex.

If anyone of these systems have begun to not function as they should, they will signal a fault code to the car's main computer, which in turn will illuminate on the dash an alert notification to the driver. This is when something has gone wrong, not necessarily broken, but maybe needs investigating from a technician.

Some of these systems will function while the car is sitting still and not turned on. They will make noises too. With that, I will agree 100% that when you sit down in front of the service attendant at the dealership, you are talking to a 'layman' to some degree. They are typically not very technically inclined to any high degree, but have been trained in general terms to understand the basics of car functions.

Moving up from the service person is where the challenge begins, managers are usually very busy dealing with many situations throughout their day. As such, a complaint about an unfamiliar noise with no sign of a fault code or dash light or message displayed equates to a very low level issue to them. The car's not broke, not telling the driver 'I have a problem' it's essentially indicating that 'all systems go!'.

If the noises are persistent, happen at specific times when specific actions happen, yes explain that to your dealer, hopefully they will take the car and try to replicate the concern and advise what they find.

I hope this helps, I'm not trying to be rude, just want you to see their side of the scenario. Be patient, kind and understanding. Yes we all have dealt with dealership service departments that have been quick to respond and not take your concerns seriously. Your warranty is there to protect you too. If something is truly not right it should eventually get resolved.