Lite load flutter

[denpaw]

Thrilled with service at Mazda until... At 27K there was enough smoke coming out the exhaust that it caught my eye- Took it in, and of course, all of the "black box" readings were "normal". They threw an O2 sensor at it and I don't think the smoke is as bad but ever since there is a flutter feeling (that varies) under moderate throttle between 3400-4000 RPM. Again with the "normal readings", spoke to the "District Service Mgr" who drove the car and acknowledged the condition- They sent some Mazda Diagnostic specialist- he described the problem as "feeling like a fish nibbling" and he would be checking it out. Got a call later that day and was told "everything checks out fine, this is NORMAL for this powertrain" And, of course, when I asked to speak with the Mazda guy, he had already left.

I'm COMPLETELY Dissatisfied and like a paper cut, this is a CONSTANT annoyance driving the car- Is everyone else experiencing this? Any guidance on what I can do to force satisfaction

HELP!!!
Denny