Lochinvar Boiler Rough Ignition, Bangs.

New unit ~1.5 years old, installed by others, been having rough ignition since it was installed. The prior company tried to solve the issue by replacing the venting. Needless to say I double checked that the intake and exhaust pipes are clear and with no sagging. It vents out the side of the house. Total run is about 35 feet which is well within the 100 foot maximum for 3 inch venting. Separate pipes - no concentric. Gas valve has been replaced: CO2, O2, and CO are all within range according to manual and tech support. New ignitor. Burners removed and cleaned. Exchanger clear. Condensate trap and drain clear. Static gas pressure starts at 7.3" wc and drops to somewhere around 6.5". Manifold draft pressure also good (can't remember what that was, but tech support said it was good). Circuit board and ignition cable replaced. Inspected venturi - good. If you look closely at the video, you can see the flame shoot through the condensate trap. Any help much appreciated.

Model: WHB199N