Unreliable VOIP, Arris 502G, Comcast

Switched from Residential to Business to try to obtain reliable, reasonable quality VOIP. In 2 weeks, have hung up on people, xx(x) dB(?) hard scratching noises during calls, when I listen to voicemails left by my phone to another phone, there are breaks, changes in tone. All cabling from new Arris box to street replaced by Comcast. Neighbor's cabling theoretically corrected that was inducing minor jitter per tech rep. Customer support can see, after 2 weeks of services, numerous resyncs, 30 power adjustments in the past 2 days automatically by the modem because it is "increasing the power of its communication with the station due to poor receipt of CMT broadcasts".
At this point, they just had me measure the power to make sure it was within 110 - 120 Volts going into the model. It's 122 V if one believes that my fluke is calibrated properly. That shouldn't matter. It's steady, it goes thru a power protector, I'm measuring out of the power protector that is used by the power plug that goes into the modem. THis is the third or fourth modem but first since swapping from residential to business. There is one modem for the phone, another separate modem box for the broadband internet.
Downstream QOS can be poor, max delay is typically quite long. packets dropped can be 0 - 100%.
Customer support typically claims that line quality is excellent but the debug level of the techs varies so much that often I don't think they're trained well enough to debug this issue. Tech support online notes are never read by the techs sent tot he house.
Thanks if you know where to troubleshoot.