Knocking from below.

Looking for ideas. Got a kinda knock from below when driving. Bit like going over these slowy down strips on the road.
Initial thought was propshaft joints, front just recently done and rear seems ok with a cursory quick shake albeit without it jacked up so far. Checked wheel nuts, all good.
So, any ideas where to look next please.
Thanks.

I had that and it was a missing lower damper bush on the front. On strip down I also found the axle mounting for the damper had gone oval.
It could be a multitude of things though. Best bet is to find a method of replicating the noise at stand still while looking underneath. I found mine by bouncing on the front bumper.

repair pic to show where the mount is.

Cheers @Flossie. Checked them, no joy. Propshaft sh****d so removed. Replacement too long. Eventually found right one and fitted this morning. Test drive.......still knocking. Back under to check all tightened properly (well at my age you never know).
Sliding out spotted bulge on inside of n/s rear tyre so loaded up spare set of General Grabbers and set off to get them changed. (£50 for swap & balance 5 tyres!!! What a deal.)
Well, fitter showed me tyre. Big chunk missing from centre of tread about 3" x 2" wish I'd thought to take pic. Fitter reckoned problem with tyre as couldn't explain it otherwise.
Driving home and surprise, surprise no knock.
Grateful I'm still alive and still shocked at the carnage I could have caused.
Will now check treads too rather than just sidewalls.