Vilaskadival said: “In my opinion, all initial sense inputs are neutral..”.
That is true except for the sense inputs coming through the kaya indriya (physical body).
– Vipaka of past bad kamma bring bring bodily pain (headaches, injuries, cancer and other other diseases, etc).
– Vipaka of past good kamma bring bring bodily pleasures (any pleasurable bodily sensation like a good massage, etc).
Details at, “Does Bodily Pain Arise Only Due to Kamma Vipāka?“.