My bonneville keep maaking an funnt noise when i pick up speed

Check the heat shield on exhaust converter

Since it should be under factory warranty I would expect you to take it to the dealer for inspection.
My first guess would be something in the exhaust or the suspension.

Check to see if one of your brackets holding the exhaust pipe has come loose. That'll make a rattling sound - especially if it towards the end by the tailpipe. When you're accelerating - more air is forced thru your exhaust at a faster rate, so it's not moving as much as when you're sitting still and the truck is just at an idle with less air/exhaust moving thru the tailpipe. If it's only making the noise while the truck is stationary & the noise stops one the truck is moving - that pretty much rules out anything to do withe the drive-train or suspension. You are sure the noise is from the back & not coming from under the hood? If under the hood - check your oil level ASAP.

IF YOU HEAR RATTLING NOISE IN SUPER CHARGER.YOU HAVE WORN DRIVE MECHANISM LIKE LOOSE ROTOR SHAFTS OR WORN ROTOR SHAFT BEARINGS.

It amazes me that they didn't at least address the rattling noise, seeing how they probably caused it. If it is just a belt, that's an easy fix. Did you stop at another shop & ask for a quick diagnosis?
Could be something as simple as a heat shield , or something. Doesn't hurt to have a second opinion, and shouldn't cost anything, or very little, then go back & tell them what the diagnosis was.

had the same issue, had someone look and it seems the noise was caused by heat shield being loose covering exhaust system. Have that checked out.

probably the strut (shock)

not likely possibly the cover for torque converter may be loose. if rattling coming from pass. side may be belt tensioner/or water pump. to check shut engine off remove serp. belt check water pump pulley for play by wiggling back an forth do same with belt tensioner. check trans fluid level while on level surface engine warm&running tranny in park. some gm cars have had problems with crank shaft pulleys making rattling noise also.

sounds to me like the heat sheild on the exhaust!! simple enought to fix!!! no harm to get car serviced while your at it to

If its a 5 speed i would say check ur throw out bearings on ur clutch.