I have a strange noise coming from somewhere under the hood that I just can't identify. It sounds/feels like a a strong vibration but at the same time it sounds really nasty. The strangest thing is the timing of when it happens, only between 2500 and 3500 RPM's no matter what gear, right in the limbo between coasting and acccelerating or if holding withen that range. I.E. cruising at a given speed, and letting up on the pedel slightly to maintain speed, as long as the RPM's are in the range I mentioned I hear the noise, but if it is higher or lower nothing.

Sounds like it is possibly one of your motor mounts. When my front dog bone mount took a shit on me it made the motor vibrate like hell around 4,000 rpm's.

That is really weird if it is, I just had the engine swapped in May (threw a rod in my other SR) and had prothanes put in all the way around. I will check that out as soon as I get the chance though.

If you had prothanes put in then I highly doubt that is your problem. Can you describe the sounds a little more. Maybe where you think it would be coming from?

It sounds like a harmonic vibration bordering on a grind and it sounds like it is coming from somewhere midline, which makes me think tranny, but I have no other issues with the tranny. What you said about the engine mounts made me think of a couple other things I can check and maybe work on, I will have to see what my McGyver braistorming session will come up with.

put big washers on each of the cross member bolts.. take one bolt off go to home depot an get a washer thats big enough for that bolt.. i say youll need 8 washers 2 on each bolt... wanna test it to see if this is whats happening on your car.. park your car on a parkin stump makin the crossmember be pushed up then rev it an tell me if you hear the noise again

Turns out that is what it was thanks a lot, the front bolts had a wierd spacing going on. They were uneven as well, so what I did was make some rubber spacers and put them on, works well enough and there is no more vibration from them.

Buuut (isn't there always a "but"?) now that I can hear my engine again, lol, there seems to be another wierd noise coming from there at almost the exact same RPM range. The only differance is that I can replicate the problem without being in gear. It is coming from somwhere near the injectors/intake manifold (Highport). Any ideas?

Ok to be a bit more specific, the noise again almost sounds like a harmonic vibrating, only occures between 2250 and 2500 RPM's, has a decidedly metallic sound to it, and to sounds like it is coming from near the injectors/intake manifold. May even possibly be towards the timing chain side. It is really hard to identify an exact location, but it is rather troubling, hope it is not something serious.

Pop your valve cover and look at the timing chain guide. Sometimes, the timing chain gets slack in it and it hits the upper timing chain guide and can make noise. I don't think it would give vibrations though. Just a thought.

Actually that is what I was thinking as soon as I heard it, read about it elsewhere on the forum, but I just wanted to get other peoples opinions before I go chasing ghosts in the machine. If it is the guide, and I remove it, I would have to get one of the new tensioners correct? Either way I will pop it off as soon as I get the chance and take a look.

http://www.sr20forum.com/showthread.php?t=88199

Yea that is the thread that I saw, sooo it looks like I have a little bit of a project on my hands, guess it will have to wait till I have a little bit more time on my hands. Thanks a lot for the info and assistance guys.