You're right that the word comes from Old Norse. The words that come from the North are always the most colorful in English. You understand its meaning but it doesn't work in this sentence for grammatical reasons. "Berserk" is an adjective, not an adverb. An adjective cannot modify a verb. In this sentence, it is being used to modify the verb "rattle", so that is an error. It is OK, though, as an example of colloquial English.

I would say '. . like mad', which is what 'berserk' means. If someone 'goes berserk' they are very agitated or angry, or they are behaving in a crazy way. I didn't know about the Viking warrior reference - it's interesting.

It just means it is shaking it around a lot. Could change berserk to crazy.