99 Windstar knocks when compressor runs

My 99 Windstar (3.8 engine with 118000 miles) sounds like a diesel engine when the AC compressor kicks in. I replaced the ac compressor thinking it was the clutch going out, but the noise continues. Seems to be a knocking noise from the lower front/timing chain cover, but can't imagine why the timing chain would only knock while the AC is running. All ideas welcome....

I found out where mine knock was coming from. Follow your belt around until you see the tensioner which is at the back (fire wall side). At low idle with the air conditioner running the tensioner will vibrate making knocking sound.

Hmm,

My 98 ticks when the AC is on. I wonder if that is the similar. Did you have to replace the tensioner or just the belt?

Thanks

I sprayed it with wd-40 (lubricant) over time fill with dirt and stuff cause friction.

Thanks for the advice....you were right, it is the tensioner. I would have been looking forever. I greatly appreciate it. Who would have thought it could make that much noise.

I know it sounds like a diesel engine at a stop. Did you lubricate it that took mine away.