  Causal soliton formation (e.g. oscillons, Q-balls) in the primordial Universe
is expected to give rise to a universal gravitational wave (GW) background, at
frequencies smaller than scales of nonlinearity. We show that modifications of
the soliton density field, driven by soliton interactions or initial
conditions, can significantly enhance universal GWs. Gravitational clustering
of solitons naturally leads to generation of correlations in the large-scale
soliton density field. As we demonstrate for axion-like particle (ALP)
oscillons, the growing power spectrum amplifies universal GW signals, opening
new avenues for probing the physics of the early Universe with upcoming GW
experiments. Our results are applicable to variety of scenarios, such as
solitons interacting through a long range Yukawa-like fifth force.
