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.

Factory Service Manual

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).