KM n-grams:
唸り声	2912
唸声	11
呻り声	29

Quite odd. There may have been a lot of pages with it back in 2007. Nearly 1/3 of the count was for 唸声中国.

gg5, daij
唸り声を	        17,847		
唸声を	        28
唸り声が	        6,254		
唸声が	        144

I think something is distorting the n-grams for 唸声. The top terms look odd. It does get 36 hits in Aozora, though.

@@ -27,0 +28 @@
+<gloss>growl</gloss>
@@ -29 +30 @@
-<gloss>growl</gloss>
+<gloss>snarl</gloss>
@@ -32,0 +34,2 @@
+<gloss>hum (of a machine, power lines, etc.)</gloss>
+<gloss>drone (e.g. of an engine)</gloss>
@@ -34,2 +37 @@
-<gloss>hum (e.g. motor)</gloss>
-<gloss>whistling (e.g. wind, wires in the wind)</gloss>
+<gloss>howl (of the wind)</gloss>

Good one. 唸声 is in Unidic and JLD.

〈呻（り）／唸（り）／うなり〉〈声／ごえ〉

Google N-gram Corpus Counts
╭─ーーーーー─┬────────┬───────╮
│ 唸り声　　 │ 39,831 │ 36.7% │
│ うなり声　 │ 35,812 │ 33.0% │
│ 唸声　　　 │ 32,183 │ 29.6% │ - add
│ 呻り声　　 │    371 │  0.3% │ - add (nikk)
│ 呻声　　　 │     64 │  0.1% │
│ 呻ごえ　　 │      0 │  0.0% │
│ 呻りごえ　 │      0 │  0.0% │
│ 唸ごえ　　 │      0 │  0.0% │
│ 唸りごえ　 │      0 │  0.0% │
│ うなりごえ │    354 │  0.3% │
╰─ーーーーー─┴────────┴───────╯

Surprised to see 唸声 with so many counts. Judging by a google search, it seems to have this reading.

@@ -3,0 +4,3 @@
+<k_ele>
+<keb>唸り声</keb>
+</k_ele>
@@ -8 +11,6 @@
-<keb>唸り声</keb>
+<keb>唸声</keb>
+<ke_inf>&io;</ke_inf>
+</k_ele>
+<k_ele>
+<keb>呻り声</keb>
+<ke_inf>&sK;</ke_inf>