polo 9n vibration

hey, ive recently put th seat sport brace and pd 160 intake on my polo tdi 130, but now say your driving slow , sub 20, around 1.5 2k when de- gassed, theres a horrible vibration the brace doesnt appear too catch the bulk head, but its got me very confuzzled!

any one else had this, or any remerdies?

cheers danny