I have not experienced this on any of the local AMs here in the Baltimore/Washington area, so I'm not sure how widespread this technology is.
The
worst sounding AMs here are the low-budget operations like WTRI 1520 Brunswick MD (17KW day timer) with their "Radio Asia" Indian music satellite format that sounds like a Napster-era MP3. Perhaps their transmitter is very old and under-maintained, and I doubt they're running their licensed 17KW.
I can say, without a doubt, the
best sounding local AM in my listening area is WHVR 1280 Hanover PA, (5KW day/500W night), currently doing a classic hits format with the liner "Happy 95.3 & 1280." Their rig sounds like Timtron built the exciter and processing.
Without a doubt, crappy technology like Voltair is hurting AM and hastening its demise.