I have a 2012 F-sport model and the hybrid fan next to the rear passenger seat gets real loud after about 30 min of driving. We recently took a 100mie trip and it was annoying us the whole day. When i took my other lexus for service and got a CT loaner, i took another trip. This one was 140 miles and the fan didnt make a sound. Any ideas?

 

Something Lexus reset?

 

I had similar issue last summer, my hybrid fan was getting very loud after start, and won't be quiet.
I restart the car and the fan became quiet and normal, this happened twice totally.

I took my CT to Lexus dealer, the technician did complete hybrid system check, but couldn't find anything abnormal.