Strange 'cracking' sound from front of car.

I bought a 225 last week, on the test drive, when pulling away, and at low speed driving, there was an occasional knocking sound, which doesn't happen at high speed. Presuming it was a drop link or similar I wasn't concerned and used it to bargain the sale price down.

Ive had the car jacked up and can't find any play in the suspension arms, track rod ends, wheel bearings etc..

I did notice the car had purple springs, and before posting this had a look through previous threads and noted that some lowering spring kits are prone to making clunking sounds?

Any hints what else it could be if not springs?

TIA.