Clunking noise front passenger side when braking

[Jsbrooks2]

(2002 boxster) Ok so yesterday morning I left the house and noticed at slow speeds when braking I heard a clunking type noise coming from my front passenger side. I immediately pulled over went to inspect under the car to see if somehow I was dragging something then went to the tire inspected as best I could to see if anything was rubbing or loose etc nothing. I took it to my mechanic who got into the car with me I drove it he noticed it as well he thought it was something loose in the trunk which when we check the spare was loose however we drove and still noticed a noise. He put it up on the lift checked joints bolts rotors caliper breaks etc can’t find anything wrong I looked at the forum’s and brought up what I’ve seen on here but he still hasn’t found the cause of the noise. I left the car at the shop to see if he could figure out what it could be he was ready to let me take the car I was worried it was brake related so told him to reinspect the vehicle anyone have some suggestions???