Most likely it is because of the bad exhaust - the conditions you describe are "lean run" conditions, and leaks in the exhaust will cause "lean pops" - actually the opposite of the usual backfire, but the same effect - A new exhaust system SHOULD cure the problem.

An especially entertaining example of this phenomon is seen on old aircraft piston engines - the pops from those monsters can really wake you up!

Ed <eduntz@HOTMAIL.COM> wrote:
Not sure if this has been a problem for a while, and I'm just noticing it more because my exhaust is going, or if it's new, but here's what I'm experiencing- when I'm letting off the gas, or, especially, when I'm coasting down a hill with my foot off the gas, I get a noise, sometimes just a loud popping, but sometimes, as in going down the hill, it is quite a loud backfire. When shifting manual trans gears, I hear a bit of the popping, but when going down a hill at about 3,000 RPM, the noise is quite a backfire.

Could this be associated with my worsening exhaust, or is is likely unrelated? I'm trying to get the exhaust done in the next week or so, so I guess I'll see how noticeable the noise is after that if I don't do anything else.

Thanks,
Ed