Your car doesn't have cam phasers. These are a part of the variable valve-timing feature found on the 3V 4.6L engine. The 2V has "fixed" cam timing.
He may have been referring to the timing chain tensioners though. However, you said that you heard the sound coming from the "Passenger side rear part of the engine" which probably rules out the timing chain hardware since that's all located under the front cover of the engine.
You said the sound started after you moved from MO to TX. As well, the car's only got 25K miles on it: Problems from the timing chains or tensioner hardware on such a youthful engine would be the last thing I'd suspect.
I still think it sounds like detonation. Have you tried running a can of NOS octane booster through it to see if the noise goes away? Again, did you check the torque on the spark plugs yet?
(BTW, the reason I keep mentioning NOS is because it's one of the few that I've tried that actually worked, at least for me. It got rid of a nasty throttle tip-in burst-knock resulting from very aggressive timing in my N/A tune/combo before the blower.)