These units have volume adjustments for speaking and listening. Sometimes adjustment pots get dirty and sticky, especially outdoor units. Try cycling the adjustments then tweaking them. You may have some audio clipping going on.

The included VP324-D power supply IS a filtered power supply according to Valcom's website...the 624 provides 600 ma as opposed to the 300 from the VP-324-D, which requires 250 ma so you need a VP-324 for each door phone. or a 624 to power 2 door phones.

Try cycling and adjusting the pots.

Sometimes the thoughts in my head get so bored, they go for a stroll through my mouth. This is rarely a good thing.