Is this good for a VC4 500 (corexy atm)?

So a first resonance test of my vc500 (corexy config) gave me this as a result. As you can see their are three problems: -first vertical bit is quiet small (don't know if this really is a problem); -between 75 and 100Hz, the upper belt has a small jump (should I reduce the tension on the upper belt?); -at higher frequenties, their is also a small jump (Does it mean their is something loose in my toolhead?). Can someone confirm if my solutions are right? And does anyone happend to know that my first problem really is bad? Thanx in advance :)!