If it is perfectly ballanced at the CG (about 4 1/8 from the LE of the wing), and all other things seems to be in order I can think only about 2 things:

1. (easy) try to trim elevator a little bit - just to see if it hels in any way.
2. (hard) is it possible that the firewall is NOT PERFECTLY perpendicular to the "ground" or may be engine is mounted slightly tilted upwards? If tis is the case I guess I would advise the same thing the guy from the club told you - do not fly this model until you can somehow fix this problem.

Good luck!