Any wheel in particular? (Find small bump and aim one wheel at a time at it.) That may help narrrow it down to one wheel (Shock absorber mount, anti roll bar, suspension mount) or one axle (anti roll bar, suspension mount) etc.
Some enthusiastic rocking of the car while parked may throw up some clues
You may also get some mileage by parking with two wheels one side on the kerb (HANDBRAKE!!) which may give you enough room for a furkle underneath. (Watch out if you ask someone to rock the car whilst yo are underneath)
Failing that, pop down to Kwikfit etc., and ask them to pop it on a ramp