Need help with Mold smell

Hoping for some help here for anyone with experience with mold...

I'm looking to buy a house, it's a new build, local builder, very reputable.. the house is perfect... except it stinks!

details
- newer build (about 5 years old)
- small family live there, apparently really reclusive
- did a walkthrough of the house first time and LOVED everything but the smell
- agent said this smell wasn't an issue before and since he's visited the home called it an isolated occasion.

decided to proceed with an offer, of course based on a thorough home inspection, hired a guy who specialized in mold just in case, was hoping that the smell was a one off thing, but was trying to go in prepared...

during the home inspection
- we started outside, all was well, hairline crack in the foundation was the only point to mention outside, he said it was small and very common...
- opened the door and sure enough same smell
- we started in the basement, all systems okay... evidence of water in the furnace, HRV was a bit dirty and seamed to have not been opened in awhile... once we did the systems we decided to investigate for the smell...

- spent over an hour in the unfinished basement doing moisture readings... in the basement we found
- builder installed cold room was dry and smell free (odd, but good)... there's been a lot of rain lately so sump pump pit had some water.
- bottom step base had a slight moisture reading (just over 17%) near the floor
- bottom step base had some slight pink staining from surrounding insulation... this possibly coincides with a hairline foundation crack on the outside... investigating, home is under warranty, so this wouldn't be the end of the world, builders would fix without issue
- only drywall in the area was nearby this, we got home owners permission (yes this was a real home inspection) and cut a large piece of drywall out in that section... no obvious mold found, no dampness found... just evidence of a previous leak.. area tested dry
- everywhere else in the basement read dry as a bone... we tested the studs/wood along the concrete just about everywhere along with multiple places in the area where that showed some water markings... no moisture, no obvious mold, smell was no stronger in these areas than anywhere else
- moisture readings on both thermal and moisture meter (pin/non-pin) were at or below standard... other than the base of the one step there is NO dampness in that basement (or anywhere else in the home)

- at nowhere in the basement could you pinpoint the smell... it was just everywhere.. somewhat stronger in the basement (to me) but definitely noticeable on all levels

Once we left the basement it's noted that there's no screens on any window and they are no where to be seen... it's winter and they may have removed them for the staging (this home was staged so beautifully), but it's mentioned by the agent that these people rarely go outside. (she's an interning doctor, he's an engineer, they have a pre-school age daughter)

rest of the home inspection was VERY uneventful,

inspector noted that the HRV didn't seem to be properly communicating with the furnace and that it needed to be (re)balanced... also found two loose toilets that were not leaking but should be tightened..

home inspector noted everything is WELL ABOVE code... was very impressed... (e.g. builder put an attic over the garage AND insulated it...) they did a great job he said and he can't figure out the issue..

- described the property grading as "Wickedly awesome" and hoped that if there was a foundation crack it could be repaired inside easily since it would be a shame to disturb that...

when we cut into the drywall, the builder came to the door (this is a smaller town so when one call went out, someone must have called the builder)... he said the place was way too humid when he walked in (we had been testing furnace and all of that as part of the home inspection, so possibly that).... he also said the HRV was not installed by him and the owner must have installed...

we did air quality testing on every level (home inspectors idea and at his cost.... he just hated not knowing what was going on)... awaiting results, but even if there is a problem (which our noses tell us there is), we aren't all that much closer to actually finding it...

now I am FAR from an expert in any of these things but I am a good at scouring the internet and finding all sorts of articles on things...

here's the theory I've come up with... the mold is somewhere in the HVAC system... would explain why it's detectable everywhere and yet everything is dry.... these people are not opening windows and they are not getting in and out enough to circulate air properly.. HRV is not balanced and probably not working....

anyone else have any other theories?

I want to buy this home, but I don't want to buy the smell..