I am new to biking. I bought a hybrid bike with 9 gears at the back tire and 2 gears at the front. For reference lets say gears at front (chain ring) are numbered 1-2 and gears at back are numbered 1-9. As the numbers increase the the cycle becomes harder to pedal (for both front and back). For example if you switch from 1 to 2 at front cycle is harder to pedal. And if you switch from 2 to 3 at back tire, the cycle is harder to pedal.
Now my question is this. Are there certain gear combinations, I should not be using. Can you write those combinations down for me like (1 back, 5 front). So I can use that for reference. The particular problem I am having is that when I am at around 7-9 at back and 1 or 2 at front the cycle starts making a weird noise. Is it normal? Any other combination I should not use?