From the air handler to the vents you have positive pressure. From the return grills to the air handler you have negative pressure. Check the return ducts and make sure they are all taped. Applying mastic to all joints in the system in not a bad idea either.
Like to reinforce this.
All seams should be sealed with glass cloth and mastic, not tape, which is at best a temporary fix.
If you do use tape, use aluminum tape, not “duct tape”