fMRI repetition time (TR) and stimulus duration
(f)MRI does not have good temporal resolution. If that is needed something like EEG or MEG is used, but the latter have low spatial resolution (hard inverse problem). 
Also note that the low temporal resolution of fMRI is due to BOLD response time (i.e. it's not just the case  that the current fMRI technology sucks)


  fMRI’s temporal resolution is limited by hemodynamic response time; typically the BOLD response has a width of ~3s and a peak occurring ~5–6s after the onset of a brief neural stimulus. This is much slower than the underlying neural processes, and temporal information is thereby heavily blurred.


Without getting into the specifics of the experiment (what's that you're actually trying to measure) it's impossible to say whether fMRI (=BOLD) would be inappropriate.

Also noise and blur are not the same issue; loot at some illustrations and it should be obvious without getting into math.