I have a 99 ZX2 that when running at idle soulds like I have a pool of frogs under the hood. Every now and then a squeel like a belt squeal would sound and then go away. I replaced the belt but the noises still exist. For some reason I was frustrated and trying to find this mystery noise and I removed the oil filler cap and lots of air pressure exited and the noise went away. As soon as I put the filler cap back on the noise returned. I thought I was imagining it so I repeated the procedure with the same results. Now I am wondering if anyone has experienced this and could maybe point me in the direction of what's needed to repair or what could be wrong. I am thinking there is some sort of valve regulator gone bad, like an EGR type valve but not sure.
Any help to this backyard mechanic is appreciated.
Thanks