I would suggest that the words "heavy duty" applied to a machine sold for less than $150 is probably taking a little bit of artistic licence.
Grosgrain edging is very stiff so you will probably need at least a 100 size needle for this and they may well go blunt pretty quickly. This could be the squeaking noise, needles will "pop" and squeak if they are blunt. Change the needle and see if it stops.
I would suggest that if you are doing straight stitching in large volumes for commercial purposes, this is not the right machine, you need something like a Singer 20U industrial machine, a good workhorse which will do straight and zig zag stitches.
I have one of these with a 3/4 hp motor in a table and it is so strong, great for sewing tents, horse blankets etc. We used it for attaching vinyl to 1/2" foam for ride-on tractor seats, something it did really well. Different needle system to domestic machines and can sew heavier gauge thread too.
Sorry, this probably isn't what you wanted to hear about your new machine. Try changing the needle and see if it stops the squeaks. But you may need to reconsider your choice of machine.