Check the wheel rim for a hairline crack. Not easy to see usually, so remove the wheel would be my advice. If you inflate the tyre (tire) to around 40psi cold then try the soapy water dip with the whole wheel. But don't dunk the wheel bearings into the water. Just the rim as you turn it very slowly. I've found many a cracked wheel rim that way. You only need a big bowl of water. You will find it! Good luck.