When I had my PS3 fixed, they just sent me a refurbished version of the same model (launch EU 60GB) so I would assume M$ does that, though I did think they had a new motherboard designed to go into old broken 360s

Lol.  "reduced massively"?  The only report the public has on Falcon RRoD issues comes from a report stating that 10% of Falcons sold had been returned for this reason after only 3 months on the store shelves.  The 30+% RRoD rate of the Xenon was reported after nearly 9 months of data -- I would wager that the Falcon is not much different... probably less, but 10% is a bare minimum.  Some data has gone on to show that, to date, the failure rate of the original Xenon is now over 60% -- I suppose then, a likely 20-25% LTD failure rate on the Falcons might qualify as "massively reduced", in that regard.

RRoD won't be out of the picture until the Jasper motherboard hits the shelves sometime this month, or early December.  MS would be foolish to replace a RRoD console with anything *but* a Jasper mobo, going forward.  A billion USD only goes so far, when it comes to replacing defective hardware.  

OP: You had a Xenon.  They gave you a Falcon (likely a Falcon V3, which has a better layout than the V1, with regards to heat), or you may have lucked out and gotten an early Jasper.  They don't want to replace your next RRoD if they can help it.  You can bet that, with the introduction of the Jasper motherboard, MS will tend to replace your console, rather than repair it, if you had a Falcon, Opus, or a Xenon.  The last iteration of the Falcon is supposed to be decently reliable (but it was only in production for a couple months, until they ran out of 90nm GPUs), so in some cases, MS might send those as replacements, instead of a Jasper.

i recieved a refurb back that makes a "twang noise" even when it isn't on. (since other electronics in the canbinet have fans that make the 360 slightly move)

but all hope is not lost, I just picked up Fallout 3 and the Orange Box, (for $25) since i never had a chance to play all of that game last year. ... All for the 360.

But my confidence was forever shaken when it RROD'd, and with the annual payment of LIVE coming up for me... the 360 better keep going strong, or this is the last payment of live or the last games I will ever buy for it.

@OP, you are lucky to get a nice one back... and in 9 days too!
mine took 7 weeks for the whole process.

When I got mine back, it was the same serial number, but it is loading much faster.