Noisy When Heater Is On

[DHP]

My coworker has a Lexus ES-something. He knows that I work on my own car (not a Lexus) and am fairly knowledgeable about my own car, so he asked me what's up with his car. He said yesterday when he turned his heater on, it started making a lot of noise. He showed me what he was talking about and he's right. When the heater is on, it sounds like he has an exhaust leak. That's exactly what it sounds like. But why only with the heater on?

Any ideas? All input is appreciated. I'd like to help him out. I'm supposed to come by his house tomorrow and look at it in the daylight.

This is a 1st gen ESxxx with 200,000+ miles (I think 217,000).

[gbhrps]

Any time that I've heard a heater fan make any kind of noise that wasn't normal it usually was a bearing/bushing that had gone bad in the fan motor shaft, or debris of some type( leaves, maple keys) that had gotten into the air intake and was lodged next to the fan blades and was being struck by the blades as they spun. I suspect the same is true with your friend's situation. The only way to be sure is to pull the fan assembly from the HVAC and track it down. This is not a feat for the faint of heart.

[camlex]

what happen when he use AC?

[DHP]

Shockingly, when I checked the oil in the daylight there was none on the dipstick. I know he doesn't take very good care of his car but I thought he was smarter than that. It took a few quarts and now it doesn't make the noise at all... very strange. I have no idea what the oil had to do with the heater. He's lucky he didn't end up with serious damage.