Thumping noise

[93geoprizm]

So there's been this thumping noise comin when im going straight. Doubt its the axles but there was a lil wiggle on the passenger side when we had the car up. Also noticed the front mount cracked which will be replaced soon. My mechanic said something that it could be the differential goin bad? I was like we have differentials??? lol
It like every revolution of the wheel theres a boom, but not too loud so it gets faster as i go faster.
Any guess on what it could be?

[93geoprizm]

Small update.
So my mechanic told me that once they lifted the car, they saw the problem. Rear strut/shock has gone bad and was leaking fluids. This cause excessive wear on the tire which is why the tire is making that wierd thumping noise. Now I have coilovers, not like I can to a autozone and grab me one. im thinking of just buying a cheap tire for now and just replacing it for the time being. Im not sure how long has that coilover been bad for since I saw no difference in driving and cornering. You think it should be ok for the time being. I am just thinkin of slapping my stock suspension once winter rolls around and selling the coilovers.

Another problem I had was the gas line. The thing is rusted to heck and my mechanic noted it leaking gas and told me to get it replaced asap. Where can I get these from?

[94PrizmDD]

I had bad struts for almost a year till i replaced them lol. You cant order a replacement strut for your coil over?.