Which one can be considered correct depends on the intended meaning of
Both sentences have the same structure:
haben + adverb + verb in Partizip II
That structure sets the whole action in Perfekt.
The difference in meaning is the result of the fact, that two different verbs are used.
gemerkt is Part. II of the verb merken and means something along the lines
perceiving something emotionally, observingly, noticing something
Partizip II of bemerken is bemerkt.
According to dwds the meaning is a little less specific than for merken.
Bemerken means just
perceiving sth. / so.
and is therefore not limited to an emotional jugdement of the real-world observations.
Bemerken is perceiving something observable.
Merken is dealing with it emotionally.
Please consider @Janka's answer regarding a flaw in both variants if it comes to being correct or not.