Mazda 5 Knocking in Engine

I have a Mazda 5 with about 85,000 miles - I just took it to an auto mechanic and they think I need an engine replacement. Ugh. I took it for a second opinion and the mechanic said they could do some exploring in the engine if I paid by the hour and see if its something they can fix.

So I'm hearing a knocking sound after start-up at idle and at low rpms. And as I press the gas, the knocking sound gets louder and sounds more like a flapping sound or a playing card in the spokes of a bike but once above maybe 3-4k RPMS the sound goes away. From my untrained ear it could be coming from the passenger side of the engine. The KBB value is somewhere around $4500, which is pretty much what an engine replacement is going to cost me.

Can anyone give advice on where to start or maybe where to direct the mechanic if I try to put some money into it. I'm not sure I want to sink any money into it at all and I might just junk it and see what I can get. Any suggestions would be appreciated.

Like a lifter type noise? What would help make the decision for a new engine is if you admitted to any neglect. Didn't change oil for too long, drove on an oil leak, drove on an overheat? If any of that is true I would pass on the repair and opt for engine swap or just junk it. Otherwise 85k isn't that old maybe have them do some exploring.

Google/YouTube "Mazda VTCS", get mechanic's opinion.