Depends on form
The heavy feeling usually indicates a lack of stability or proper form. Everything is important in order for you to be properly setup.
Taking it out of the rack is very important. Your upper back should be a solid rack; your elbows should be under the bar, and then you should arch out of the rack like doing a goodmorning, and not push it up and out with your legs. Your steps back should be exact. Before descent I always mentally cue myself, chest up and knees out.
If you approach each weight and treat it equally, then this setup will be natural. Warming up with the bar should be done exactly as your last set would be done.
My abs are my weak spot that I have to constantly improve upon, so when I squat without a belt, I feel the heavy instability feeling you talk of. With the belt on, I have good stability so that the heavy feeling is not as pronounced.