1994 BMW 318 Fishtails at Hwy speeds

Hi,

I have a 1994 BMW 318IS. I may have 2 problems or a combination of one problem.

When driving hwy speeds, the car fishtails.

Also when going over bumps, the car hits it with a bang. I think it is more from the rear. I suspect the rear shocks but I do not see any leaks.

Please assist.

Thanks,

Michael