  Recently, pulsar timing array (PTA) collaborations, including NANOGrav, have
reported evidence of a stochastic gravitational wave background within the nHz
frequency range.\ It can be interpreted by gravitational waves from preheating
era. In this context, we demonstrate that the emission of this stochastic
gravitational wave background can be attributed to fluctuations occurring at
the end of inflation, thus giving rise to the Hubble tension issue. At the
onset of inflation, the value of the frequency of the gravitational wave signal
stood at $f=0.08nHz$, but it rapidly transitioned to $f=1nHz$ precisely at the
end of inflation. However, just before the end of inflation, a phase
characterized by curvature perturbation is known to occur, causing a swift
increase in the frequency.
