I have an HQ Avante 18 purchased in July 2011. I have completed over 80 quilts on her, and have logged 6,500,000 stitches. I have oiled her regularly as recommended with the changing of the bobbin. She is making a sort of "metal on metal" grinding sound especially when running slowly. Is there a recommended frequency for maintenance service performed by a technician? I do plan on discussing the need for a trip to the shop with my local HQ dealer. In the meantime I am interested in the company's perspective. Thank you.