Caller with Grand Cherokee making "bonk sound"

The 93-99 Grand Cherokee has coil springs in the rear with a 4 link link suspensionsion with panhard bar (so technically a 5 link). The panhard bar is commonly called track bar.

Most likely it is not a spring making the sound, but the track bar shifting due to a wallowed out bolt hole on either the axle end or the frame end bracket holding it.

No personal experience with the Grand Cherokee, but lots with Comanche and Cherokees which (along with the Grand Cherokee and 97 and newer Wrangler) uses a similar suspension in the front, and this is a very common problem on them.