So, first post on here, sorry for it being a problem. I usually try to help a few people on these forums a few times before I go asking for it, but this one has me stumped. I've got a 98 GTP with 154k on it, and it has developed a funny rumble at idle. It's not there when the engine is cold, but as soon as it hits about 160 degrees it starts to show up. I've tried recording it, but it's too quiet for my phone to pick up, and the really weird part is that you can't hear it under the hood, only inside the car. The best way to describe it would be that it sounds like a pot with a lid on it when the water starts to boil, just kind of a rythmic rumble. The next development has been that there is the occasional popping sound that comes with it, almost sounds like microwave popcorn. It'll do it maybe once or twice, stop for a few seconds, do it again, not do it for a minute or so, do it again. Totally random. The rumble goes away as soon as I touch the throttle, and the popping goes away after about 1500 rpm. No drivability issues, no idle issues other than the noise, and no starting or power issues. I got one check engine light for a camshaft position sensor, replaced it, and no change other than gaining 2 mpgs. Totally stock motor with the SLP air box. Love this car, and I'm just trying to keep it in as good of condition as I can. Any ideas? Any help would be great. Thanks in advance.