GQRX Frequency tuning
It is common for low-cost direct-conversion (zero-IF) RF receivers to have a DC offset in their A/D hardware, which would correspond to a large spike at the frequency that you're tuned to. That's probably what you're seeing in the waterfall display, as some models of RTL2832U receivers use zero-IF architectures. 

For what it's worth, for such a cheap device, I'd say the above is actually pretty good from a DC-offset perspective. You can work around it by tuning slightly away from the signal that you want, then apply the residual frequency offset yourself in your signal processing (it looks like that's what your SDR software package is doing).