I was at my mechanic's shop last night and he noticed that my belt tensioner shock has broken loose from one of its mounting points and needs to be replaced. I ordered the replacement today but I’m wondering, what is the function of this shock? My friend said that without it, when I accelerate I may get a rumbling sound. And, in fact, I’ve had this sound for a while.

Thanks

------------------
1985 190e 2.3 5spd
98 E320 rims + TV & VCR
1991 Mazda Miata
1991 Yamaha FZR1000
1994 MB S420 (sold)
1994 BMW 318ica (sold)