Strange Knock 2001 GT

[GTowner2016]

So, I just upgraded from a very crappy 2002 Grand Prix SE to a 2001 Grand Prix GT. I get this car, and no sound, suddenly it's having issues. While idling, nothing at all. If it's idling you give it gas and it gets about 1200 rpm's then it starts a slight knocking noise. When on the road in 1st and 2nd it knocks, but higher gears, where it's not under strain, it makes no knocking. It does have two loose motor mounts I have to get around to. New front struts, tie rods, recent oil and filter change and alignment. Not sure what it could be. Transmission was rebuilt 25k miles ago (very smooth shifting). It's not a lifter as I experienced that with my SE, and it started as soon as it was started, this doesn't. Any ideas?

[Fivefingerdeathpunch]

Need video of noise when you rev it.

[GTowner2016]

Will try to get one real quick.

[GTowner2016]

Perfect timing, my phone gave out before I could get the video. Here is the best I can describe it. It sounds like a slight lifter tick in idle, its shallow until the motor warms up real good, then it's a deep hallow knock. It's worst in 1-2 gear, but once in 3rd it's alot quieter (more like a lifter) and the car gets up and goes. It's just the deep hallow knock when it's under the strain of taking off really.