I found out that the windshield I have on my car has been replaced by the previous owner. I keep on hearing wind noises... Seems like it leaking into my car from the windshield! is it normal?

 

leaking? like water leaking?
if so, you better have it check asap!

 

When the windshield was replaced, was it replaced with the OEM windshield or some aftermarket one?

 

OEM windshield will be stamped with the LEXUS logo in the lower passenger side corner of the glass (just like the other windows)...factory glass is insanely expensive, so most likely it is aftermarket...

When replacing the windshield on the IS, if you don't know what you are doing it is very easy to break the tabs on the side moldings, and most people will just glue them back or just try and place them back without...only option is replacing the moldings and re-sealing the glass, but sometimes the glass can break when trying to take it out, so you will probably be looking at a quote to replace everything...dealership will not help if it is not LEXUS glass...

Sorry man, but call around for estimates, it is probably not as expensive as you think...GL