New Bike, Reputable LBS, So what is the Problem?

I have a 3-week old bike, a Roubaix Elite 27, that I purchased from what
is supposedly a reputable dealer in Manhattan.

I've tried pretty hard to support the LBS, buying quite a few accessories
there, not moaning that they forget my club dicount, etc. It's expensive,
but convenient and, well, these shops have to make ends meet, so why
not?! One tries to establish some goodwill.

A couple of days ago, the left crank started to 'jolt' whenever it passed
the eleven o'clock position. Not on every turn, but let's say, six times
out of ten and right across the cassette and chain-rings (i.e., not
specific to any gear).

I waited until I thought the LBS would not be busy then took the bike in
for inspection. It was quite clear that no one wanted to look at it.
Eventually managed to get a mechanic to spin the rear wheel and fiddle
with the derailleur adjustment. I explained that I failed to see how that
would stop the left-hand crank from jolting (it happened at the same crank
position, regardless of gear or chain position, etc.). No joy: they
clearly weren't interested in helping further. Said I could leave the
bike there for ten days so that they could do a 'full check-up'.

And I certainly wasn't asking them to tighten cables and polish the seat
for me. My only concern was this crank/bracket anomaly.

So, at the same time I'm paying over the odds for lubricants, cleaners and
a cadence monitor for my Polar device (another $70). Still, no interest
in looking at the bike.

I assume it's the LBS's responsibility to sort this out, but I am
reluctant to press the issue as the last thing I want is a p*ssed-off
mechanic playing around hastily with the bottom bracket on a bike rhar's
cost me well in excess of $2,500 (including bits and pieces, tax, etc.).

I'd be happy to go and pay a few dollars for another shop to sort this
out, but, frankly, I have no idea which places are good. And I cannot
guarantee I'll get any better service!?

So, my question is: will my LBS refuse to touch the bike if I have another
shop look at this particular problem? And, if not, does anyone know a
decent LBS in Manhattan who could sort this out in a few hours.

Any thoughts on how to handle what I assume is a common challenge for
people who buy new bikes would be appreciated. Thank you.

Glm