3500 rpm noise/rattling

[BiG_HiT]

Hello everyone.
Just bought a 03.5 MSP in the begining of June. In the last month, I went to the dealer to replace the exhaust manifold gasket. Some time after, I noticed a vibration/rattling at 3500rpm. The car is completely stock and still under waranty and has 65K Km (40K miles). No matter how hard I push the accelerator , the vibration starts at 3500rpm in any gear and stop right after 3600rpm. The sound seems to be coming from the engine bay. I did use the search fonction abd saw a few threads about engine mounts and heatshield rattling so I went to check this out but everything seems OK.
Do you have any clues before I go to the dealer ?
Thanks in advance !

 

[bentegviz]

mine does it at 2500rpm, hoping someone knows what it is, i don't have the luxury of the warranty, and i don't want to take it in somewhere and have them make up things.

 

[BiG_HiT]

mine does it at 2500rpm, hoping someone knows what it is, i don't have the luxury of the warranty, and i don't want to take it in somewhere and have them make up things.

I went to the dealer yesterday. The problem was a leak coming out from right after the muffler. The dealer would charge me 400$ to change the whole thing. I went to a performance shop this morning and got it TIG welded for 85$ CDN.
I don't have any clue why the leak was only audible at this precise rpm but checking your exhaust line might be a good start.

Oh, I forgot to mention. My car is still until waranty but (of course) all the exhaust system components are excluded. And the previous owner did replace that piece a year and a month ago (so the one year waranty from mazda is gone).