If they messed with the connections coming into the house (which includes the grounding block), why would you think it couldn't be a ground loop? If they changed anything with the ground, then it absolutely could be getting a ground loop now.

I would check and see if the cable is still grounded at the DEMARC (point of entry). Check both ends - the ground block where the cable screws in and where the ground wire attaches to the house ground.
If all looks good, temporarily disconnect the ground and use your DMM to measure any voltage difference between the ground block and the ground wire. Remember to reconnect the ground.
Next disconnect the cable line and measure across the center conductor and shield for any DC voltages.

If all that looks good, install a Jensen ISO on the cable box's coax input and see if the noise goes away. If it does, check and see that all the channels still come in and leave the ISO in place if it does.
If the noise is still there, this will require a much deeper dive and time.
Could be a defective cable box, swapping this box with another one in the house could be revealing.