you know the four bolts that connect the driveshaft to the diff? Ya i lost one and replaced it with a non matching bolt thinking it would be fine, but my rear end is buzzing a lil and I figured it wouldnt hurt to try

 

If you have another of those bolts, put it diagonal from the current replacement. If you still buzz, it is probably something else.

 

I used 4 different nuts/bolts to put my 1.8 swap on the car... no wierd noises. I bought the right bolts from partstrader though... they are hardened and designed for the usage.

 

ya, well maybe i should bring this up in the forum proper then. After searching miata.net, it seems somewhat common and my chasis has 230k on it