scoobertron

hi ive had a vibrating noise coming from somewhere on my my99 its not the heat shields as theres none on it it seems to start when you let off throttle anywhere above two and a half thousand revs the warmer the car the louder it gets ive had a new gearbox new clutch and flywheel new exhaust all this started before the new parts any body got any ideas cause its doin my ed in