Engine sounds like a sewing machine at idle

My elderly parents bought a 2011 Equinox with the 4-cylinder engine in it that sounds like a sewing machine at idle. It was used with about 14K.

The dealer blew me off saying it was supposed to spound like that at idle because the ecotech engine uses low fuel pressure at idle or soemthing, but I wanted to get another opinion. This particulare Chevy dealer doesn;t have the best repuitation for service.

From what I've read on here, this may be a common problem, but I am unclear as to what the fix is. Thank you for your time.