Is it a knock, clunk, or a creaking sound?
This sound you hear, is it coming from one wheel in particular and exactly what does the sound imitate? Couldn't be a moving brake pad moving in it's holder, could it? It could also be a strut rod mount or wheel end mount moving as the pressure increases.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan