Just curious, where did you get this line? The words don't seem to fit well. Either due to error in typing (typo), grammatical error, or maybe poetic license?
"Himig" --> tune, sound, music, melody
"Lulan" --> carry, load or ride (as in a bus, boat, or any vehicle); this is usually followed by the object that is carrying the load (e.g., lulan ng sasakyan--> carried by/ loaded in/ riding a vehicle)
"Tanto" --> realize, understand
"Ang paghimig na lulan" --> The melody that is brought/ carried...
"na aking pinagtatanto" --> ... that I am trying to understand.
I hope this enlightens you a bit. Taken out of context, the statement might not make much sense.